FIG. 1 is a prior-art block diagram of a wireless base station 100. The wireless base station 100 is typical of those used in cellular telephone and data distribution systems. Such base stations typically employ large, expensive antenna arrays 120 capable of directing the beam path to fill a desired area of coverage. Consequently, the antenna array 120 is typically shared between a base station transmit chain 130 and a receive chain 140. The radio frequency (RF) output signal from the transmit chain 130 traverses a duplexer 150 to arrive at and be radiated from the antenna array 120. Received signal RF arriving at the antenna array 120 is routed by the duplexer 150 to the receive chain 140.
The transmit and receive chains of modern wireless base stations operate on different frequency channels. The duplexer 150 passes RF energy from the transmit chain 130 to the antenna array 120 and simultaneously passes received RF energy from the antenna 120 to the receive chain 140. Theoretically, the duplexer 150 does but does not pass transmit RF energy to the receive chain 140. In practice, however, the duplexer rejection requirement is quite high due to a dynamic range between the transmitter output power and receiver sensitivity that can typically exceed 150 dB. Duplexers currently employ expensive, bulky, high-order filters in order to meet these stringent rejection requirements. Relaxing the rejection requirement at the duplexer 150 imposes correspondingly high linearity requirements on the receiver front-end, including on the low-noise amplifier (LNA) 160.